Image display systems which provide a stereoscopic viewing impression are already known. These systems operate preferably in that each eye is offered a different color. The stereoscopic viewing impression is then however not very pronounced in most cases. A preferred area of application is in vision testing systems.
Optical test charts and vision testing devices are disclosed, for example, in U.S. Pat. No. 4,415,243 with which a patient is tested for the monocular and binocular vision functions. This check is performed in that the patient looks through a polarization filter in front of each eye at plates illuminated with light having mutually crossed directions of oscillation. These plates have regions with different polarization actions so that the patient can recognize different regions with both eyes. The optical test charts have the disadvantage that the intensity of the luminosity is dependent upon the surrounding luminosity and that, for each test, a plate must be moved manually. Vision testing devices avoid these disadvantages since the plates therein are illuminated from behind and a switchover to another test takes place by remote control with a plate exchange taking place mechanically in the apparatus. The known optical test charts and vision testing apparatus have the common disadvantage that the plates cannot be changed by the person conducting the test without considerable difficulty since the production of the plates is very time consuming.
U.S. Pat. No. 4,870,486 discloses a virtual stereographic image display system wherein a polarizer and a liquid-crystal cell are mounted forward of an image-display surface of a TV-monitor. The light emanating from this image-display system is viewed by a viewer through polarization spectacles with the individual lenses of the spectacles having different polarization axes. This image-display system requires a large space because of the monitor and simply serves to generate virtual stereoscopic image.
A color liquid-crystal image-generating arrangement is disclosed in U.S. Pat. No. 4,877,309 which operates with two liquid-crystal image-generating cells. Two color polarizers are disposed in front of these two image-generating cells and, in addition, a neutral polarizer is disposed at the light-incident side of the first image-generating cell.
This color liquid-crystal image-generating arrangement generates only color images and, taken by itself, is unsuitable for a vision testing system for testing the binocular vision functions.
Published German patent application 3,043,511 discloses an arrangement for testing the function of the eye and of the vision system. The visual display takes place by means of monitors and is for the binocular testing with two monitors having polarizers or with one monitor (red-green stereopsis). This arrangement requires a large space and is usable only in a limited manner for vision testing when using only one monitor.
Furthermore, the arrangement with one monitor provides no stereoscopic viewing impression.
The images generated by the image display system should include letter characters, numbers, symbols, signs, pictures and the like.